1. Field of the Invention
The present invention relates to a thin-film thermal head for use in a thermal recording operation, and more particularly to improvement in a thin-film thermal head incorporating a resistance heating layer and a conductive layer.
2. Description of the Related Art
A thin-film thermal head 1 which is a subject of the conventional technique and the present invention, as shown in FIG. 2, incorporates graze projections 2 formed in a line facing the central axis 0 of rotation of a platen 3. When a recording material 4 has been inserted into a space between a platen 3 and the graze projections 2, the graze projections 2 corresponding to an image, which must be printed, are selectively heated. Thus, the image is, through a toner ribbon 5, thermally transferred to the image receiving surface of the recording material 4.
FIG. 3 is an enlarged cross sectional view showing a portion in the vicinity of the graze projection 2 shown in FIG. 2.
As shown in FIG. 3, the graze projection 2 incorporates a projecting graze layer 22 formed on a ceramic substrate 21. Moreover, a resistance heating member 23, a conductor layer 24 and a protective layer 25 are laminated on the graze layer 22. The conductor layer 24 is sectioned at the top surface of the graze layer 22 such that the two sections are formed away from each other for distance A so that a pair of electrodes is formed. When an electric current is supplied to a space between the conductor layers 24 which are the pair of electrodes, the resistance heating member 23 generates heat. The graze projection 2 is structured to cause the resistance heating member 23 between the conductor layers 24 to generate heat to record an image on the recording material 4.
The conventional thin-film thermal head has the structure that the conductor layer 24 is made of aluminum (Al). However, Al having somewhat high resistance suffers from a problem because a conductor layer having low resistance is required so as to be adapted to a thin-film thermal head having a resolution higher than 600 dpi because the recording density has been raised in recent years.
As an element having resistance lower than that of AL, Cu is a known element. When a conductor layer is constituted by using only Cu, the density can be raised because Cu has low resistance. The conductor layer made of only Cu, however, raises a problem in that separation of the film frequently occurs when, for example, the temperature is high. Thus, manufacturing yield deteriorates.